1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a shallow trench isolation (STI) process of a semiconductor device.
2. Description of Related Art
STI techniques have turned into important isolation methods in advanced semiconductor processes since STI structures occupy less areas and provide better isolation effects as compared with conventional field oxide (FOX) structures formed with the local oxidation method (LOCOS). A STI process in the prior art is described as follows.
Referring to FIG. 1A, a pad oxide layer 110 and a silicon nitride mask layer 120 are sequentially formed on a substrate 100, and are patterned subsequently. A trench 130 is then formed in the substrate 100 with the patterned silicon nitride mask layer 120 as a mask.
Referring to FIG. 18, a silicon oxide liner layer 133 is thermally grown on the surface of the trench 130, and then a silicon nitride liner layer 140 is formed on the substrate 100. Thereafter, CVD silicon oxide is filled into the trench 130 to form a STI structure 150. The filling process (not shown) comprises depositing a CVD oxide layer on the substrate 100, performing an annealing process to densify the CVD oxide layer, and then removing the CVD oxide layer outside the trench 130. During the annealing process, the silicon nitride liner layer 140 serves to reduce the stress in the substrate 100 around the trench 130.
Referring to FIG. 1C, the silicon nitride mask layer 120 is removed with an etchant such as hot phosphoric acid. At the same time, however, the silicon nitride liner layer 140 is easily over-etched to form indents 152. Therefore, the isolating effect of the STI structure 150 is reduced, and a leakage easily occurs in the channel.
Accordingly, this invention provides a shallow trench isolation (STI) process that is capable of protecting a silicon nitride liner layer in the trench from the etchant used for removing the mask layer.
A STI process of this invention is described below. A patterned mask layer, such as a patterned silicon nitride mask layer, is formed on a substrate, and then a trench is formed in the substrate with the mask layer as a mask. A portion of the mask layer around the trench is then removed, and a portion of the substrate around the top portion of the trench is removed with the remaining mask layer as a mask. A liner layer is formed in the trench, and then the liner layer on the top portion of the trench is removed with a pre-deposition process of a high-density plasma chemical vapor deposition (HDP-CVD) process. Thereafter, an insulating material like CVD silicon oxide is filled into the trench covering the liner layer remaining in the trench, and the mask layer is removed with an etchant. In the STI process, the liner layer comprises a material that can also be etched by the etchant for removing the mask layer, and can be a silicon nitride liner layer capable of reducing the stress in the substrate around the trench during a densification process of the insulating material.
In another STI process of this invention, a mask layer having an opening therein is formed on a substrate, and then spacers are formed on the sidewalls of the opening. A trench is formed in the substrate with the mask layer and the spacers as a mask. A thermal oxide layer is formed on the surface of the trench with a thermal oxidation process, such that bird""s beaks are formed under the spacers. A liner layer is formed in the trench, and then the liner layer on the top portion of the trench is removed with a pre-deposition process of an HDP-CVD process. Thereafter, an insulating material like CVD silicon oxide is filled into the trench covering the liner layer remaining in the trench, and the mask layer is removed with an etchant. In the STI process, the liner layer comprises a material that can also be etched by the etchant for removing the mask layer, and can be a silicon nitride liner layer capable of reducing the stress in the substrate around the trench during a densification process of the insulating material.
Since the liner layer on the top portion of the trench is removed in the aforementioned STI processes of this invention, the liner layer remaining in the trench is covered by the insulating material and isolated from the etchant during the step of removing the mask layer. Therefore, the isolating effect of the STI structure is not reduced, and a leakage does not easily occur in the channel
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.